Purification of tar acid-bearing oils



Patented Sept. 8, 1931 UNITED STATES PATENT OFFICE SOLOMON GAPLAN, or BROOKLYN, NEW YORK, AssIeNoR T COMBUSTION UTILITIES CORPORATION, or NEW YORK, N. Y., A; CORPORATION OF MAINE PURIFICATION or TAR ACID-BEARING OILS No Drawing.

ties which render them unsatisfactory or make them undesirable for certain, uses. One form in which these impurities manifest themselves is in the production of colored compounds when such oils are used for the manufacture of disinfectants,- animal dips, sa-

ponified cresol or tar acid solutions and repl'ated products. After exhaustive and thorough investigatlon of the chemical compositions and properties of these colored compounds their origin has been traced to certain '25 strongly reducing ortho-dihydric tar acids, similar to but not including catechol. Thus one of these bodies has been isolated and identified as a new homologue of catechol comprising 3, 4- or 3, S-dimethyl catechol.

The primary object of the present invention is to provide a process for removing color producing compounds of the type referred to from tar acid-bearing oils containing them.

Heretofore in preparing and refining tar acid-bearing oils of the class described for use in the manufacture of disinfectants, animal dips and similar products, the oils have been subjected to washing treatments with aqueous sodium carbonate solution. This treatment,

however, fails to give even approximately complete removal of the color-forming mat ter except with oils which contain unusually small amounts of such color-producing bodies. In treating other tar acid-bearing oils washing with dilute caustic soda solution has been employed, but this treatment involves a very considerable loss of the desirable tar acids of high germicidal value, which 7 are extracted togetherwith the color-forming materials by the caustic soda treatment. An:

Application filed September 22, 1926. serial No. 137,173.

other method has been recently proposed for removing these color-producing compounds from coal tar distillates and the like, which comprises washing the oils with aqueous solutions of weakly alkaline buffer agents such as calcium hydroxide and ammonium hydroxide. While this latter method of treating the oils has proved to be much more satisfactory than methods now in use in the trade, it has been found that the action of the alkaline buffer agents is often incomplete in the case of tar acid-bearing oils containing appreciably large quantities of color-producing matter. Fractionation of the oils with rejection of the portion boiling above 230 C. has also been advocated, but since this excludes the larger portion of the oil, including most of the high boiling tar acids which are the most valuable gerinicides present in the oils, the method is not commerically feasible.

Another object of the present invention is to provide a process by which the color-producing bodies present in such tar acid-bearing oils can be cheaply and completely extracted without also removing valuable tar acids.

A process for purifying tar acid-bearing oils to remove color-forming bodies which involves washing or extraction with some treating agent is usually attended with some difficulty and expense in satisfactorilydisposing of the extract from the washing or extraction treatment, for reasons hereinafter discussed. Moreover purification of tar acid-bearing oils by washing or extraction methods heretofore 'el nployed has often proven to be relatively expensive because of the comparatively high cost of the treating agent used and because the extract from the extraction treatment has been treated as a waste product. p v

Another object of the present invention is to provide a. process for extracting color-producing bodies from tar acid-bearing oils wherein the extracting agent after once being used may be rcvivifiejd at a small expense and repeatedly reused in the process.

With these and other objects in view the invention consistsin the process for purifying tar acid-containing Oils hereinafter described and particularly defined in the claims.

Essentially the process forming the subject of the present invention, in its preferred form, consists in extracting the tar acid-bearing oil with an aqueous solution of borax. Other combinations of boric acid and an alkali may be used in place of borax. It has been found that the borax in aqueous solution exerts a strongly preferential or selective solvent action on the color-producing compounds present in the oils. This solvent action is due to the fact that the ortho-dihydric tar acids which constitute the colorforming material combine readily with boric acid to form complex acids which are highly ionized and hence are strong acids. Once this complex compound or group of compounds has been formed it can be readily separated from the weak monohydric tar acids by means of a weak alkali. Borax, by reason of its hydrolysis in aqueous solution, produces both the Weak alkali and boric acid which are essential to this process. The concentration of hydroxyl ion in the solution of borax is too low to remove the tar acids of high germicidal value, so that a very sharp and selective action on the color-forming bodies is produced by the action of the borax.

The following procedure was followed in treating several thousand gallons of an oil containing thirty percent valuable tar acid bodies, said oil having been produced by distillation of a commercial low temperature tar and containing very much more of the colorforming material than is usually encountered in tar refining practise. The oil was agitated for one hour with two-thirds of its volume of a 3% aqueous borax solution, the mixture being heated at the same time to a final tem perature of 60 C. This heating caused rapid separation of layers on cessation of the agitation. The lower aqueous layer was withdrawn and the oil given another wash in the same manner. This second aqueous extract solution was then re-employed as the first wash of another batch of oil. The twicewashed coil required no further treatment. The reaction apparently is completely effective at room temperature, but it has been found that the stratification of oil and aqueous layers is more rapid and sharp at higher temperatures, and accordingly.temperatures in the neighborhood of 5060 C. are preferred for efficient operation. The oil may be distilled either before or after the treat mentif desired, although such distillation is not necessary for the removal of the colorproducing bodies.

It has been found that the dihydric phenols which are removed from the tar acidbearing oils by the above treatment are rapidly converted to red oxidation products upon exposure of their borax extract solution to the air. The weak alkali of-the borax apparently catalyzes this oxidation. The rapid formation of the red oxidation prod ucts upon the exposure of the borax to air makes it very diflicult to dispose of the borax extract for the reason that the deep red color rapidly discolors any stream into which the borax extract may be run as waste matter. Since the chief item of the cost of the borax method of purifying tar acid-bearing oils consists in the cost of the borax treating agent, an important feature of the present invention consists in the steps employed for effecting the removal of the dihydric phenols from the aqueous borax extract containing them, so as to permit of the ready disposal of the extract and/or of its re-use in extract ing further amounts of tar acid-bearing oils. Research work on this problem has shown that the color-forming ortho-dihydric phenols and also their red-oxidation products can be completely removed from aqueous borax solution by addition of suitable amounts of a soluble ferric salt such as ferric chlorid. The ferric salt oxidizes the col oring matter and then forms a ferric compound with the oxidation product, this compound being a black flocculent water-insoluble solid which can be filtered oil from the borax solution. The black solid ferric compound thus formed is of course far simpler to dispose of as a waste product than is the red colored borax solution. Since treatment of the borax extract with ferric salt leaves the purified borax solution with aslight acidic reaction, it is necessary to add some alkali to the solution to restore the original hydroxyl ion concentration and to neutralize any acid which may remain in the solution. This latter treatment would necessitate a second filtration for removal of the precipitated iron oxids from the borax solutionwere it not for the fact that according to the present invention both precipitations can be performed at approximately one and the same time, so that only one filtrato the aqueous borax solution which has become saturated with color-forming bodies extracted from tar acid-bearing oils suitable amounts of a soluble ferric salt and of an alkaline agent, agitating, and subsequently separating the insoluble.precipitates formed from the revivified borax solution by settling and filtration. The clear filtrate which is recovered by this treatment has been found to be as satisfactory for purifying tar. acid-bearing oils as is the fresh borax solution. V l e The borax revivification steps, of the present invention are not limited in their application to the use of any one particular iron salt or alkaline agent, nor to the use of any par ticular quantity of either agent nor to any specific time of agitation or settling, nor to any specific method of separating the precipitates and the clear liquid. Since ferric chlorid is a relatively costly material it is preferred to employ a cheaper source of ferric iron than the chlorid, such for example as an oxidized copperas solution. The following procedure is set forth as an example of a satisfactory method for revivifying borax extract of the character obtained in accordance with the extraction steps of the present invention. To an aqueous borax solution or extract which has become saturated with color-forming bodies removed from tar acid-bearing oils originally containing them there is added ferric chlorid or other ferric salt either in the form of asolid or of a concentrated solution, the quantity of ferric salt used being such that there shall be 2.1 grams of ferric iron per gallon of the borax extract. The mixture is then agitated for several minutes to insure a thorough distribution of the iron salt and to allow the black precipitate to form. A quantity of calcium hydrate or other alkaline agent is then added in amounts equivalent to 4.7 3 grams of calcium hydrate per gallon of the saturated borax solution. Agitation is continued until the lime has all dissolved.

The mixture is then allowed to stand for at least one hour, this being necessary for the reason that the complete precipitation of the iron hydroxids from the mixture is relatively slow and if any iron is allowed to remain in the borax solutionit will act to prevent complete extraction of the color-forming bodies from tar acid-bearing oils subsequently treated with the recovered borax solution. Most of the solution can then be decanted, care being taken that none of the precipitate is in cluded. The remainder of the solution is then filtered, preferably with the addition of a small quantity of some filter aid (such for example as activated carbon), and the clear filtrate and the decanted portion can then be combined and used for the purification of further batches of tar acid-bearing oils.

It is not intended to limit the scope of the present invention to the treatment of oils containing definite percentages of color forming and non-color-forming compounds nor to the use of definite proportions of extraction agent, nor to the employment of particular temperatures or particular time limitations of agitation, or particular methods of separating the oil and aqueous layers. The process is applicable to the treatment of a tar acid fraction alone (unadmixed with hydrocarbon oils), and satisfactory results are obtained by using widely varying proportions of extraction agent at normal temperatures.

Vhile the treatment of tar acid-bearing oils of the class described with aqueous borax solution is preferably followed by one and sometimes. two washings with further amounts of extraction agent in order to remove the last traces of the color-producing polyhydroxy compounds, these latter washings are not absolutely necessary except when residual oils of extreme purity are desired. When the first extraction with aqueous borax solution is followed by one or two additional washingswith further amounts of the extraction agent, the volume of extraction agent required in the second and subsequent washings to completely purify the residual oil is small compared to the volume employed in the first washing. The volume of extraction agent used is preferably limited to that required for removing the color-producing impurities.

By employing the process forming the subject-matter of the present invention for the purification of tar acid-bearing oils, disinfectant emulsions can be prepared from soap base blends of the oil which will not turn pink and the purification of the oil can be completed ata relatively small expense without materially lowering the value of the disinfectants and germicidal agents prepared therefrom. a

The term tar acid-bearing oil is used in the description and claims to describe shale oil, low temperature tar oils, vertical retort tars, coke oven tars and all liquid oil condensates derived from coal tars and the like. The tar acid content of such oils-often consists almost entirely of compounds which, while they resemble the phenols in some of their properties, do not come within the gen erally accepted definition of a phenol but are rather hyclroxyl derivatives of cyclic hydrocarbons which are non-aromatic in character, having hydrogen and alkyl side chains attached to the nucleus.

The preferred form of the invention having been thus described, what is claimed as new 1. A method of eliminating color-producing compounds from tar acid-bearing oils containing them which comprises agitating the oils with an aqueous borax solution in amounts insufiicient to neutralize and remove therefrom tar acids of high germicidal value present in the said oils, settling, and separating the aqueous extra-ct containing the i said color-producing compounds from the residual oil still containing tar acids.

2. A method of purifying tar acid-bearing oils containing color-producing substances which comprises agitating one volume of the oil with a smaller volume of an aqueous borax solution, suspending agitation and allowing the aqueous layer to settle from the residual oil, and separating the aqueous extract containing the said color-producing substances from the purified residual oil containing the tar acids.

3. A method of purifying tar acid-bearing oils containing color-producing compounds which comprises agitating the oil with an,

14 teases-e2 aqueous borazk solution in amounts insuflicient to remove therefrom desirable tar acids of high germicidal value present in the said oil, settling, separating the aqueous layer containing the said color-producing compounds from the. oil. containing tar acids and subjecting the residual oil sti-llcontaining tar acids to at least one additional Washing with aqueous borax solution.

4. A method .of purifying tar acid-bearing oils containing .color-producing compounds which comprises agitating the oil with a smaller Volume of aqueous borax solution, applying heat to the mixture during agitation, settling, separating the aqueous layer containing the said color-producing compounds from the residual oil still containing desirable tar acids of high germicidal value, and subjecting the residual oil to washings with aqueous borax solution.

5. A method of purifying tar acid-bearing oils containing color-producing .com pounds comprising agitating one volume of the oil with a smaller volume of a 3% aqueous borax solution for a period of about 1 hour at a temperature of about 60 C., subsequently settling and separating the aqueous layer containing said color-producing compounds from the residual oil, agitating the residual .oil with aqueous borax solution, settling, and

separating the aqueous layer from. the purified oil.

6. A method of purifying tar oils containing tar acids and coloreproclucing bodies to adapt the .oils for use as disinfectants, which method comprises agitating the oil with a dilute aqueous solution containing an alkali metal compound capable of dissolving in an aqueous solvent to yield an alkaline solution containing a boric acid radical thereby selectively extracting color-producing compounds from the said oil, while leaving therein valuable low boiling and high boiling non-color forming tar acids.

7. A method of purifying a tar oil containing tar acids andcolonproducing compounds which comprises extracting the said oil with a dilute aqueous borax solution at temperatures in the neighborhood of to 0., subsequently settling the mixture and separating the aqueous extract containing the coloi' producing compounds from the purified oil containing tar acids.

8. A method of purifying tar oils containing tar acids and color-producing substances which comprises extracting the oils with an aqueousborax solution thereby efiecting the selective removal of the colonproducing substances from the said tar oil.

In testimony whereof I affix my signature.

SOLOMON c'AP AN. 

